I always default to “man foo”, because of the occasional tool that when presented with -h or --help creates a file with that name; even if there’s no manpage, “man foo” will never have any undesired side effects.

Nearly every tool does have a manpage (even a basic one) thanks to Debian’s manpage policy: “Each program, utility, and function should have an associated manual page included in the same package or a dependency.… If no manual page is available, this is considered as a bug and should be reported to the Debian Bug Tracking System.”

The rare times I encounter a command‐line tool that has no manpage, I’ll sometimes write one and contribute it upstream.

Of course some programs have a useless manpage that points to info. Thankfully that is pretty much limited to GNU tools which I’m lucky enough to not have to use very often.